Do you have to click exactly on the checkbox for it to activate? Or, can you just click on the containing cell? If clicking on the cell will activate the checkbox then I would suggest that you do that.

If you have to click on the checkbox, is the location of the checkbox static within the containing cell? If so, you could just use specific coordinates with the Mouse -> Click action in Ranorex and click on the cell at the coordinates of the checkbox. If the location is static, this should work.